A couple filmed in a lingering embrace on a Shanghai station platform are suing the metro rail authority after the video of them kissing was posted on the Internet.

The couple, said to be in their 20s, claimed the video posted on popular video websites Youtube.com and Ku6.com had embarrassed them and violated their privacy rights, according to the China Daily.

"We think employees of the metro station taped us illegally and made negative comments (while filming)," it quoted the unnamed man in the video as saying.

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"This has to do with the protection of the legal rights of all passengers travelling on metro trains in Shanghai, and not simply our own interests and (the) damage it has done to us."

The video shows the couple in a prolonged embrace and kiss as three voices speaking in the local Shanghai dialect can be heard in the background laughing and making lewd sexual comments.

The title of the video is "Shanghai metro line staff secretly tape lovers kissing goodbye."

The Shanghai Metro Company said it was investigating the matter.

"If it is proved the video was shot by metro company employees, they and the company should take responsibility for the invasion of the commuters' privacy," said Gao Puping, a professor of law at East China University.

In communist China privacy was virtually non-existent in the past, when the state interfered in all aspects of people's lives.

But a sense of privacy has emerged with economic reform and the retreat of the state apparatus from society.